Technical Field of the Invention
The present invention relates to seal support systems for double mechanical seals and, in particular, for double mechanical seals.
Description of the Prior Art
A mechanical seal comprises a stationary seal face and a rotary seal face energized against each other and connected to the stationary housing of a pump and the corresponding rotary shaft respectively. The seal faces are held in their respective positions most commonly by metallic components such as a gland or shaft sleeve.
A double mechanical seal has two sets of stationary and rotary seal faces, an inboard set and an out board set. There is a cavity between the two sets of seal faces and the outside diameter of the outboard faces is exposed to atmosphere. The purpose of this cavity is so that barrier fluid may be piped from a seal support system at a pressure higher than that of the product. This helps to optimize the running conditions of the seal and improve overall reliability.
Many seal support systems include a vessel which becomes pressurized when it is completely sealed and is filled with a barrier fluid. This is due to the available volume of gas within the vessel becoming compressed. This compression provides the required barrier fluid pressure which ensures the optimum running of the seal.
In some situations, the compressed gas within the vessel can be lost. This can be due to a number of factors including escape to the atmosphere through fixtures and fittings or through gas absorption, where the gas is absorbed into the barrier fluid.
When this occurs, the seal support vessel becomes completely filled with water and there is no further room for thermal expansion of the barrier fluid. This can result in, under certain situations, such as rising temperatures, the internal pressure of the system rising exponentially, leading to the pressure exceeding the maximum working limit of the vessel and potential damage to the vessel.